Vibrating barrier: a novel device for the passive control of structures under ground motion.

Cacciola P, Tombari A - Proc. Math. Phys. Eng. Sci. (2015)

Bottom Line:
The ViBa is a structure buried in the soil and detached from surrounding buildings that is able to absorb a significant portion of the dynamic energy arising from the ground motion.Numerical and experimental analyses are performed in order to investigate the efficiency of the device in mitigating the effects of ground motion waves on the structural response.A significant reduction in the maximum structural acceleration of 87% has been achieved experimentally.

Affiliation: School of Environment and Technology, University of Brighton , Brighton BN2 4GJ, UK.

ABSTRACT

A novel device, called vibrating barrier (ViBa), that aims to reduce the vibrations of adjacent structures subjected to ground motion waves is proposed. The ViBa is a structure buried in the soil and detached from surrounding buildings that is able to absorb a significant portion of the dynamic energy arising from the ground motion. The working principle exploits the dynamic interaction among vibrating structures due to the propagation of waves through the soil, namely the structure-soil-structure interaction. The underlying theoretical aspects of the novel control strategy are scrutinized along with its numerical modelling. Closed-form solutions are also derived to design the ViBa in the case of harmonic excitation. Numerical and experimental analyses are performed in order to investigate the efficiency of the device in mitigating the effects of ground motion waves on the structural response. A significant reduction in the maximum structural acceleration of 87% has been achieved experimentally.

RSPA20150075F12: Recorded acceleration of the structure subjected to harmonic base motion at a circular frequency = 22.62 rad s−1 in the case of a single structure and a structure coupled with the ViBa.

Mentions:
Experimental shake table tests are performed in order to validate the analytical formulae and numerical results determined in the previous sections. The prototype as depicted in figure 5 is designed to reproduce the system of figure 4 and is tested on a 45 × 45 cm shake table. The purpose is to show the efficacy of the ViBa, calibrated by equation (4.9), in reducing the structural accelerations. The structure to be protected is realized as a one-storey shear-type building made up of acrylic for the base foundation as well as for the storey (80.5×80.5×10 mm) while aluminium sheets (80.5×141.6×0.6 mm) are used for the walls. Additional masses are placed on the top of the structures in conjunction with an accelerometer of mass 4.2 g on the top of the structure in order to record the structural response. The interaction effects with the soil are captured by linear elastic springs leading to a total stiffness kf=640 N m−1 and kf,ViBa=760 N m−1. The SSSI is represented by a linear spring kSSSI=315 N m−1 coupling the structure with the device. The prototype is set up on a Quanser Shake Table II for performing dynamic tests. Harmonic tests are carried out at several frequencies ranging from 2.0 to 10.0 Hz considering first the structure on its own and then coupled with the ViBa. The inherent damping is quantified through a best fit of transfer functions evaluated numerically and experimentally. Moreover, the ViBa is modelled as a rigid container with an internal oscillator made up of a spring connected to a mass and placed adjacent to the structure as shown in figure 5. The ViBa has been calibrated in order to absorb the energy affecting the structure at a selected frequency, i.e. the resonant frequency in the uncoupled system, that is, ωstr=ω0=22.62 rad s−1. However, the device is efficient for whichever desired frequency, i.e. the device can be calibrated to absorb any target frequency. The optimal design is accomplished by means of equation (4.9). Namely, the optimal stiffness of the ViBa, calculated by means of equation (4.9), is for mass mViBa equal to 0.629 kg. The transfer function is derived as the ratio between the maximum acceleration recorded at the top of the structure and that applied to the shake table. Figure 11 shows the comparison of the calculated transfer function of the structure uncoupled and coupled with the ViBa. The experimental curves show the efficiency of the ViBa in altering the structural response. Moreover, numerical transfer function curves are drawn by means of equation (4.3), and show a good match with the experimental results. Finally, the RF calculated as the ratio between the maximum acceleration recorded in the coupled system and uncoupled system providesRF=max{U¨1coupled(t)}max{U¨1uncoupled(t)}=0.13.Therefore, the device has been able to reduce the dynamic response of the structure by 87%. Figure 12 also reports the structural time-history accelerations for both the coupled and uncoupled case recorded during the shake table test when a harmonic base input at the target frequency ωstr=ω0=22.62 rad s−1 with maximum acceleration of 1 m s−2 is applied.Figure 11.

RSPA20150075F12: Recorded acceleration of the structure subjected to harmonic base motion at a circular frequency = 22.62 rad s−1 in the case of a single structure and a structure coupled with the ViBa.

Mentions:
Experimental shake table tests are performed in order to validate the analytical formulae and numerical results determined in the previous sections. The prototype as depicted in figure 5 is designed to reproduce the system of figure 4 and is tested on a 45 × 45 cm shake table. The purpose is to show the efficacy of the ViBa, calibrated by equation (4.9), in reducing the structural accelerations. The structure to be protected is realized as a one-storey shear-type building made up of acrylic for the base foundation as well as for the storey (80.5×80.5×10 mm) while aluminium sheets (80.5×141.6×0.6 mm) are used for the walls. Additional masses are placed on the top of the structures in conjunction with an accelerometer of mass 4.2 g on the top of the structure in order to record the structural response. The interaction effects with the soil are captured by linear elastic springs leading to a total stiffness kf=640 N m−1 and kf,ViBa=760 N m−1. The SSSI is represented by a linear spring kSSSI=315 N m−1 coupling the structure with the device. The prototype is set up on a Quanser Shake Table II for performing dynamic tests. Harmonic tests are carried out at several frequencies ranging from 2.0 to 10.0 Hz considering first the structure on its own and then coupled with the ViBa. The inherent damping is quantified through a best fit of transfer functions evaluated numerically and experimentally. Moreover, the ViBa is modelled as a rigid container with an internal oscillator made up of a spring connected to a mass and placed adjacent to the structure as shown in figure 5. The ViBa has been calibrated in order to absorb the energy affecting the structure at a selected frequency, i.e. the resonant frequency in the uncoupled system, that is, ωstr=ω0=22.62 rad s−1. However, the device is efficient for whichever desired frequency, i.e. the device can be calibrated to absorb any target frequency. The optimal design is accomplished by means of equation (4.9). Namely, the optimal stiffness of the ViBa, calculated by means of equation (4.9), is for mass mViBa equal to 0.629 kg. The transfer function is derived as the ratio between the maximum acceleration recorded at the top of the structure and that applied to the shake table. Figure 11 shows the comparison of the calculated transfer function of the structure uncoupled and coupled with the ViBa. The experimental curves show the efficiency of the ViBa in altering the structural response. Moreover, numerical transfer function curves are drawn by means of equation (4.3), and show a good match with the experimental results. Finally, the RF calculated as the ratio between the maximum acceleration recorded in the coupled system and uncoupled system providesRF=max{U¨1coupled(t)}max{U¨1uncoupled(t)}=0.13.Therefore, the device has been able to reduce the dynamic response of the structure by 87%. Figure 12 also reports the structural time-history accelerations for both the coupled and uncoupled case recorded during the shake table test when a harmonic base input at the target frequency ωstr=ω0=22.62 rad s−1 with maximum acceleration of 1 m s−2 is applied.Figure 11.

Bottom Line:
The ViBa is a structure buried in the soil and detached from surrounding buildings that is able to absorb a significant portion of the dynamic energy arising from the ground motion.Numerical and experimental analyses are performed in order to investigate the efficiency of the device in mitigating the effects of ground motion waves on the structural response.A significant reduction in the maximum structural acceleration of 87% has been achieved experimentally.

Affiliation:
School of Environment and Technology, University of Brighton , Brighton BN2 4GJ, UK.

ABSTRACT

A novel device, called vibrating barrier (ViBa), that aims to reduce the vibrations of adjacent structures subjected to ground motion waves is proposed. The ViBa is a structure buried in the soil and detached from surrounding buildings that is able to absorb a significant portion of the dynamic energy arising from the ground motion. The working principle exploits the dynamic interaction among vibrating structures due to the propagation of waves through the soil, namely the structure-soil-structure interaction. The underlying theoretical aspects of the novel control strategy are scrutinized along with its numerical modelling. Closed-form solutions are also derived to design the ViBa in the case of harmonic excitation. Numerical and experimental analyses are performed in order to investigate the efficiency of the device in mitigating the effects of ground motion waves on the structural response. A significant reduction in the maximum structural acceleration of 87% has been achieved experimentally.